Method of making a plural parallel rod electrode cover

ABSTRACT

Methods for construction of a cover for a plural active element electrode which is produced as a single unit having plural parallel channels substantially square in cross section.

United States Patent Inventor Erllr Gustav Sundberg Osbacken, Nol, Sweden Appl. No. 864,332 Filed Oct. 7, 1969 Divlsion of Ser. No. 653,379, July 14, 1967, Pat. No. 3,503,807. Patented Oct. 26, 1971 Assignee Aktiebolaget Tudor Stockholm, Sweden A METHOD OF MAKING A PLURAL PARALLEL [56] References Cited UNITED STATES PATENTS 2,318,809 5/1943 Snyder 136/55 2,896,006 7/1959 Sundberg 136/43 2,9 72,000 2/1961 Boriolo 136/43 3,081,368 3/1963 W'u'nsche... 136/43 3,099,586 7/ 1963 Buddy 136/43 3,207,632 9/1965 Dickover et al. 136/16 3,216,864 11/1965 Bushrod et al.... 136/148 3,266,935 8/1966 Boriolo 136/43 3,462,305 8/1969 Fahrbach 136/38 Primary Examiner-Winston A. Douglas Assistant Examiner-A. Skapars Attorney-Burns, Doane, Swecker & Mathis ABSTRACT: Methods for construction of a cover for a plural active element electrode which is produced as a single unit PAIENTEnum 26 an 3,515,834

sum 2 or 4 INVENTOR ERIK GUSTAV SUNOBERG PATENTEDBCI 25 m1 SHEET 30F 4 INVENTOR ERIK GUSTAV SUNDBERG flu w, MA ATTORNEYS PATENTEfium 25 I97! 3, 15, 34

SHEEI u 0F 4 iii w 66 INVENTOR ERIK GUSTAV SUNDBERG ATTOR N EYS METHOD OF MAKING A PLURAL PARALLEL ROD ELECTRODE COVER This application is a division of my copending application, Ser. No. 653,379, filed July 14, 1967, for ELECTRODE FOR GALVANIC ELEMENTS.

The present invention concerns electrodes for galvanic elements, especially for electric storage batteries of the lead-acid type with positive tubular plates consisting mainly of a plurality of rods of conductive material connected at both ends by suitable connections, each individual rod being in contact with active material and the active material being surrounded with a novel cover or casing. The cover or casing is, in accordance with the invention, made-of electrically insulating material that is resistant to the electrolyte and to the reactions in the electrolytic cell, but which permits the passage of electrolyte while retaining the active material in place.

It has been the prior practice to make such tubular covers from a fabric of glass wool or equivalent fiber material enclosed by an outer thin walled perforated tube of a plastic foil. Such covers have also been made of a woven or plaited hose of fibrous material, which hose is treated so that it maintains its tubular form and is self-supporting. Additionally, it has been proposed, first to place active material in paste form on the conductive rods of the electrode and, after the paste has hardened, to wind a fibrous cover in the form of a band or spiral around the paste coated electrode rods.

Of the constructions hitherto introduced some have obvious advantages, while others have been replaced as being inadequately suited for actual use of the battery in its practical applications. One disadvantage connected with the prior efforts is that the electrode covers that have been found most effective are relatively expensive to produce for the reason that it is difficult to place them on the plural electrode element assemblies.

The electrode accordingto the present invention is characterized in that the covers for all the conductive rods or elements which compriselheelectrode assembly are produced as a single unit. Such a cover may consist of a number of tubes corresponding to the number of electrode rods, which tubes may be substantially square or rectangular in cross section to facilitate a side by side arrangement. These tubes may be lined on the inside with a fabric or a felt of glass wool and may in themselves be a thin-walled, perforated foil of a synthetic material such as polyvinyl chloride or polyester.

The cover according to the present invention has been found to have significant advantages compared to previously known covers. It has been found that the capacity of the electrolytic cell is higher with the use of electrodes according to the present invention for the reason that the cover requires comparatively very little space in itself, thus allowing a larger portion of the available space to be occupied by active material. The cover is furthermore simpler to make than hitherto known electrode covers, is simpler to place on the electrode, and effectively prevents the disassociation of active material from the rods.

THE DRAWINGS FIG. I is an end view of a storage battery partially cut away so as to show a portion of an electrode assembly positioned therein.

FIG. 2 is a side view ofa storage battery partially cutaway so as to show a portion of the electrode assembly positioned therein.

FIG. 3 is a side view of one-half of an electrode cut away so as to show the construction thereof.

FIG. 4 is a plan view in cross-sectional taken at line 4-4 through the electrode of FIG. 3.

FIG. 5 is a diagrammatic view to an enlarged scale of an electrode showing the parts of the outer convoluted cover that may be formed as a unitary member and used in an electrode.

FIG. 6 is an enlarged view similar to that of FIG. 5 showing the use of a layer of insulating fibers around the faces of the active material (not shown) of the electrode.

FIG. 7 is a view similar to that of FIG. 6 illustrating the use of a multiple layer of insulatingfibers fonned to have a convoluted shape and located between the individual electrode rods.

FIG. 8 is a plan view in cross section of afurther embodiment of the electrode illustrating the construction thereof by employing a plurality of C-shaped casing elements.

FIG. 9 is a plan view in cross section of three of the elements of FIG. 8 illustrating the forming of the C-shaped cover members around mandrels prior to the stacking thereof.

FIG. 10 is a plan view in cross section ofthe cover members of FIG. 9 after stacking and being compressed between two pressure plates and prior to removal of the mandrels.

FIG. 11 is a plan view in cross section of the stacked cover members of FIG. 10 with the mandrels removed.

FIG. 12 is a pictorial view of a finished electrode which is similar to that illustrated in FIG. 8, but with portions at the left side cut away'to better illustrate the construction.

FIG. 13 is a diagrammatic plan view of a cover arrangement slightly modified from that of the embodiment shown in FIGS. 8-12.

FIG. 14 is a cross-sectional view of the electrode illustrating a method of inserting the active material and bending the cover members to form the jacket for the active material.

FIG. 15 is a view similar to FIG. 14 but showing an alternative method of construction of the electrode utilizing Z- shaped elements.

FIG. 16 is a view similar to FIGS. 14 and 15 showing still a further method of construction of the electrode utilizing C- shaped elements.

FIG. 17 is a cross-sectional view of the electrode showing a construction thereof utilizing tubes of square cross section.

THE PREFERRED EMBODIMENTS Referring now to the drawings, the positive and negative electrodes are mounted within the battery case 20 and are interleaved with separators 22. If the electrodes conform substantially to the internal measurements of case 20, no additional cementing or welding of the individual cover elements is required since separators 22 and case 20 will prevent the elements from sliding apart.

Referring now to FIGS. 3 and 4, the cover 24 for the active material 36 which surrounds the electrode rod 28 is customarily a suitable plastic foil or plastic fiber felt that is as thin walled as is permissible in consideration of the mechanical stresses that can arise in the electrode. An inner insulating layer 26 of a fibrous material such as a fabric or felt of glass fibers may surround the active material 36 which in turn surrounds rods 28. Rods 28 in turn are electrically connected through a cross rib 30 which is provided with a terminal piece 32. A lower rib 34 of a material such as iron connects the rods at the bottom and is applied after the cover has been placed over the rods.

The outer cover 24 may consist of any suitable acid resistant, electrical insulating plastic material such as polyvinyl chloride, polyester or comparable material that is sufficiently porous as by being perforated to allow the necessary electrolyte circulation while maintaining the active material 36 in place; or it may consist of an equivalent fibrous material in the form of a fabric or felt.

The convoluted partitioning portion 38 of the cover as shown in the embodiment of FIGS. 5, 6 and 7 may be of the same or a similar material as that of outer cover 24. A thin layer of glass fibers 40 may, according to the demands that are made with regard to the life of the finished electrode, be arranged as illustrated in FIG. 6 where the insulation 40 is arranged only along the inner side of the outer cover 24, or as shown in FIG. 7 where the insulation 40 also follows the course of convolutions 38. The number of convolutions in the partitioning portion is of course determined by the number of individual electrode elements the finished electrode is intended to comprise.

It is the practice in the industry to have electrodes of this type consist of either 15 or 19 rods or electrode elements. The electrode cover according to the invention is without difficulty suitable for a considerably greater number of rods or individual elements without weakening the mechanical structure since the individual rods are bound together not only by the continuous convoluted partitioning portion 38, but also by the continuous outer cover 24 which, as shown in FIG. 5 and FIG. 7, may completely enclose the convoluted portion 38.

In manufacturing an electrode according to the embodiment of the invention shown in FIGS. 5, 6 and 7, convolutions may be formed in a strip of plastic foil, for example a perforated polyester foil, having a width corresponding to the length of the electrode elements. These convolutions as shown in FIGS. 5, 6 and 7 may be formed by means of any suitable tool, for example a suitable number of mandrels which conveniently may be substantially square in cross section. As the convolutions are being formed about the mandrels, the outer cover 24 may be applied with or without the insertion of the insulation layer 40. The bonding of the convoluted partitioning portion 38 and the outer cover 24 is accomplished by any suitable means which can be carried out in the presence of the insulation layer 40 such as by welding or cementing. In the welding process, the cover material 24 and convoluted portion 38 are softened sufficiently to penetrate the fibrous insulating layer 40. In the cementing process, the cement penetrates fibrous insulation layer 40 insuring thereby a good bond.

Referring now to FIGS. 8-13, a cover according to a further embodiment of the invention will be described. The same reference numerals have been used for rods 28, active material 36 and. insulation layer 26 (see FIG. 12) but the outer cover 42 is formed different from the way the corresponding cover 24 is formed in the embodiment just described.

A plurality of individual cover elements 42 are provided from a band of cover material 24 and may include a layer of insulation 26 coextensive and formed simultaneously with the cover elements 42 (see FIG. 13). A suitable method is first to join, as by means of cementing, the two bands of material of which the compound cover elements 42 and 26 is to consist, and to thereafter form the compound band around mandrels 44.

The cover may, as explained, consist of a single layer as shown in FIG. 5 or may include insulation 26 as shown in FIG. 13. In forming the elements 42, microporous material in the form of a band of suitable width may be bent under the influence of heat around mandrels 44 of the desired cross section. FIG. 9 illustrates the result of this forming step. Thereupon the mandrels 44 are carried toward each other so the free arms of the elements 42 embrace the enclosed mandrel 44 of the adjacent element 42 as shown in FIG. 10. Heating plates 46 or similar devices which are shown schematically in FIG. are pressed against the side surfaces of the cover elements, whereby the elements are pressed together for bonding.

By moistening the surfaces of the elements 42 with a solvent suitable for the material used, the elements 42 may be softened to such a degree that the applied heat and pressure effect welding of the elements 42 into a unitary structure. The bonding of the elements 42 may also be accomplished by means of a suitable cement with or without the application of heat. After bonding, the mandrels 44 are removed, whereupon an electrode cover according to the invention remains as shown in cross section in FIG. 11.

The filling of the cover 24 with active material 36 about the rods 28 may be a difficult operation depending on the consistency and other qualities of the active material 36. If the active material 36 is in the form of a dough or paste or if it consists of relatively coarse particles, it may well be impossible to fill thecover 24 satisfactorily within a reasonable time in a conventional manner. In such cases the problem may be solved as shown in FIG. 14.

The cover 24 consists of elements 42 bent at an angle of approximately 90 which may be placed in a suitable frame (not shown) so that the lower leg 50 of each element 42 forms a continuous bottom surface on which the active material 36 may be placed with the rods 28 embedded therein whereupon the upstanding leg 52 of each element 42 may be bent in the direction of the arrows 54 to enclose the rods 28 and the active material 36. The C-shaped elements 42 of the cover thus formed may then, if desired, be bonded together to form channels by means of cementing or welding as heretofore explained.

Another embodiment is shown in FIG. 15, in which a number of Z-shaped cover elements 56 sufficient for the manufacture of the electrode are stacked so that the end sections thereof form opposite sides of adjacent channels, one end of each element 56 forming a portion of one side of the cover and the other end of each element 56 forming a portion of the other side of the cover. The elements 56 so stacked may then be wrapped with a unitary flat sheet of cover material 58 as shown in FIG. 15 and abutting portions may be bonded together by means of cementing or welding by the application of vent and/or pressure as previously explained.

A still further embodiment is shown in FIG. 16 in which a number of C-shaped cover elements 60 are formed by bending a length of cover material about the three sides of mandrels and then stacking the wrapped mandrels so that the open end of each of the C-shaped elements 60 abuts the closed end of the adjacent C-shaped element to form channels for the rods 28. The stacked elements may then be wrapped with a flat unitary sheet of covering material 62 as shown in FIG. 16 and may be bonded into a unitary structure by cementing or welding after which the mandrels may be removed.

Still another embodiment is shown in FIG. 17 wherein a of square tubes 64 are formed by bending a length of the cover material around the four sides of a mandrel. The ends of the element may be, but are not necessarily secured together in the closed position shown. The tubes 64 are stacked, preferably with the mandrels in place, and the stacked elements may then be wrapped with a flat, unitary sheet of cover material 66. The abutting portions may, if desired, be bonded together prior to the removal of the mandrels.

In all of theembodiments heretofore described, the elements which comprise the unitary cover may be bonded, e.g. by welding or cementing. This bonding may not be necessary depending on the tendency of the cover material to hold its shape once deformed and the dimensions of the battery case in which it is to be fitted.

The individual channels formed within the cover for the reception of active electrode material 36 may of course be given various cross-sectional shapes without departing from the scope of the present invention. Although the square form is preferable, the channels can be made in rectangular, triangular and curved forms, whereby the side surfaces 48 of the finished cover as shown in FIG. 12 may be made planar and smooth in order to maximize the use of the space available in the storage battery casing 20.

Among the advantages of an electrode manufactured in accordance with this over the methods previously known are that a more rigid structure having greater mechanical strength is provided, a substantial reduction in the expense of manufacturing is incurred since individual electrode element covers need not be produced and a reduced time is needed to apply the finished cover to the assembly of conductive rods usually cast as a unit with the upper transverse rib.

The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent 1s:

1. The method of manufacturing a plural parallel rod electrode comprising the steps of a. forming a plurality of like cover elements into an L-shape with a long leg and a short leg by bending a length of cover material having a width substantially equal to the length of the rods to be covered at an angle of approximately 90 so that the length of the long leg is greater than the length of the short leg;

. placing the short leg of each of said elements down in a coplanar relation with the end of the short leg of one of said elements underlying a portion of the short leg of the adjacent one of the elements so that adjacent elements form upright U-shaped channels;

c. filling each of the channels thus formed with a rod and with active material to a height substantially equal to the distance between adjacent of the upright long legs of the elements; and

d. bending the portion of the long leg of each of said elements above the active material substantially parallel to the short leg of each of said elements so that the end of each of the long legs of each of the elements overlies a portion of the long leg of the adjacent one of the elements.

2. The method of claim 1 wherein the long leg of each of the elements is bent in the direction of the free end of the short leg thereof to form a plurality of nested C-shaped elements.

3. The method of claim 2 including the further sites of wrapping the nested elements with an outer layer of cover material of substantially the same width.

4. The method of claim 1 wherein the long leg of each of the elements is bent in the direction opposite to the free end of the short leg thereof to form a plurality of nested Z-shaped elements.

5. The method of claim 4 including the further step of wrapping the nested elements with an outer layer of cover material of substantially the same width.

6. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of;

a. forming convolution in a continuous length of cover material having a width substantially that of the length of the rods to be covered so that portions of the cover material extend on opposite sides of adjacent electrode rods when in use in a storage battery;

b. wrapping the convoluted cover material with an outer layer of cover material of substantially the same width; and

c. securing the convoluted cover material to the outer layer of cover material to form a unitary cover for a plurality of rods.

7. The method of claim 6 wherein the convoluted material is bonded to the outer layer of cover material by welding.

8. The method of claim 6 wherein the convolutions are formed by wrapping the cover material alternately over and under a plurality of parallel spaced mandrels.

9. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of:

a. forming a plurality of like elements from a length of cover material having a width substantially equal to the length of the rods to be covered;

b. stacking the plurality of like elements on each other to form a plurality of vertical channels so that a portion of the elements overlies the active material associated with an adjacent electrode rod when in use in a storage battery, and

c. securing the plurality of like elements to each other to form an integral, self-supporting assembly.

10. The method of claim 9 including the further steps of wrapping said stacked elements with a unitary sheet of cover material and securing the cover material sheet to said stacked elements at a plurality of locations.

11. The method of claim 9 wherein said elements are C- shaped and are formed by:

a. bending a length of cover material having width substantially that of the length of rods to be covered about the sides of a mandrel of substantially rectangular cross section, the length of said cover materials being such that the end portions thereof when bent extend beyond the sides of said mandrel, and

b. wherein adjacent of said elements are stacked so that the channel formed by the fourth side of each of said man drels and the extended end portions of said cover material formed thereabout receives the three cover wrapped sides of the adjacent one of said mandrels and so that said extended portions of said cover material of one element overlie the mandrel enclosing sides of the cover material of the adjacent element prior to removing said mandrels.

12. The method of claim 11 including the further step of bonding abutting portions of the cover material prior to the removal of said mandrels.

13. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of:

a. bending a length of cover material having width substantially that of the length of rods to be covered about three sides of a mandrel of substantially rectangular cross sectron;

b. stacking the plurality of like elements on each other to fonn a plurality of vertical channels so that the fourth side of each of said mandrels abuts the cover material on the second side of the adjacent one of the mandrels; and.

c. securing the plurality of like elements to each other to form an integral, self-supporting assembly, the first sides and the third sides of adjacent elements being substantially coplanar.

14. The method of claim 13 including the further step of wrapping the stacked elements with a unitary length of cover material and securing the unitary length of cover material to said elements prior to removal of the mandrels.

15. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of:

a. forming a plurality of like elements from a length of cover material having a width substantially equal to the length of the rods to be covered by bending said length of cover material into a Z-shape;

b. stacking the plurality of like elements on each other so that one end section of each of the Z-shaped elements are all substantially coplanor, the other end section of each of the Z-shaped elements are old substantially coplanar. and the ends of said elements abut the center section of the adjacent elements; and,

c. securing the plurality of like elements to each other to form an integral, self-supporting assembly.

16. The method of claim 15 including the further step of wrapping a unitary sheet of cover material about said stacked elements and bonding said cover material to said stacked elements at a plurality of locations.

17. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of:

a. forming a plurality of like elements from a length of cover material having a width substantially equal to the length of the rods to be covered by bending said length of cover material about the four sides of a mandrel of substantially rectangular cross section;

b. stacking the plurality of like elements on each other;

c. wrapping the stacked elements with a unitary sheet of cover material prior to removal of the mandrels; and,

d. securing the plurality of like elements to each other to form an integral, self-supporting assembly by bonding abutting portions of covlar material to the stacked elements at a plurality of locations prior to removal of the mandrels.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 615 834 Dated October 26 1971 l ERIK GUSTAV SUNDBERG It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the page containing the Abstract, after:

" [73] Assignee Aktiebolaget Tudor Stockholm, Sweden" insert:

-[32] Priority Mar. 14, 1967 Sweden 3485/67 April 21, 1967 Sweden 5617/67 Signed and sealed this 16th day of May 1972.

(SEAL) Attest:

LDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents ORM Po-1o5o 10-59 USCOMM'DC UOSTQ'PQQ 

2. The method of claim 1 wherein the long leg of each of the elements is bent in the direction of the free end of the short leg thereof to form a plurality of nested C-shaped elements.
 3. The method of claim 2 including the further sites of wrapping the nested elements with an outer layer of cover material of substantially the same width.
 4. The method of claim 1 wherein the long leg of each of the elements is bent in the direction opposite to the free end of the short leg thereof to form a plurality of nested Z-shaped elements.
 5. The method of claim 4 including the further step of wrapping the nested elements with an outer layer of cover material of substantially the same width.
 6. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of: a. forming convolutions in a continuous length of cover material having a width substantially that of the length of the rods to be covered so that portions of the cover material extend on opposite sides of adjacent electrode rods when in use in a storage battery; b. wrapping the convoluted cover material with an outer layer of cover material of substantially the same width; and c. securing the convoluted cover material to the outer layer of cover material to form a unitary cover for a plurality of rods.
 7. The method of claim 6 wherein the convoluted material is bonded to the outer layer of cover material by welding.
 8. The method of claim 6 wherein the convolutions are formed by wraPping the cover material alternately over and under a plurality of parallel spaced mandrels.
 9. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of: a. forming a plurality of like elements from a length of cover material having a width substantially equal to the length of the rods to be covered; b. stacking the plurality of like elements on each other to form a plurality of vertical channels so that a portion of the elements overlies the active material associated with an adjacent electrode rod when in use in a storage battery, and c. securing the plurality of like elements to each other to form an integral, self-supporting assembly.
 10. The method of claim 9 including the further steps of wrapping said stacked elements with a unitary sheet of cover material and securing the cover material sheet to said stacked elements at a plurality of locations.
 11. The method of claim 9 wherein said elements are C-shaped and are formed by: a. bending a length of cover material having width substantially that of the length of rods to be covered about the sides of a mandrel of substantially rectangular cross section, the length of said cover materials being such that the end portions thereof when bent extend beyond the sides of said mandrel, and b. wherein adjacent of said elements are stacked so that the channel formed by the fourth side of each of said mandrels and the extended end portions of said cover material formed thereabout receives the three cover wrapped sides of the adjacent one of said mandrels and so that said extended portions of said cover material of one element overlie the mandrel enclosing sides of the cover material of the adjacent element prior to removing said mandrels.
 12. The method of claim 11 including the further step of bonding abutting portions of the cover material prior to the removal of said mandrels.
 13. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of: a. bending a length of cover material having width substantially that of the length of rods to be covered about three sides of a mandrel of substantially rectangular cross section; b. stacking the plurality of like elements on each other to form a plurality of vertical channels so that the fourth side of each of said mandrels abuts the cover material on the second side of the adjacent one of the mandrels; and, c. securing the plurality of like elements to each other to form an integral, self-supporting assembly, the first sides and the third sides of adjacent elements being substantially coplanar.
 14. The method of claim 13 including the further step of wrapping the stacked elements with a unitary length of cover material and securing the unitary length of cover material to said elements prior to removal of the mandrels.
 15. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of: a. forming a plurality of like elements from a length of cover material having a width substantially equal to the length of the rods to be covered by bending said length of cover material into a Z-shape; b. stacking the plurality of like elements on each other so that one end section of each of the Z-shaped elements are all substantially coplanar, the other end section of each of the Z-shaped elements are all substantially coplanar, and the ends of said elements abut the center section of the adjacent elements; and, c. securing the plurality of like elements to each other to form an integral, self-supporting assembly.
 16. The method of claim 15 including the further step of wrapping a unitary sheet of cover material about said stacked elements and bonding said cover material to said stacked elements at a plurality of locations.
 17. The method of making a cover for retaining active material on the respective rods of conductive material of a plural, parallel rod electrode for use in a storage battery having positive and negative electrodes and a liquid electrolyte comprising the steps of: a. forming a plurality of like elements from a length of cover material having a width substantially equal to the length of the rods to be covered by bending said length of cover material about the four sides of a mandrel of substantially rectangular cross section; b. stacking the plurality of like elements on each other; c. wrapping the stacked elements with a unitary sheet of cover material prior to removal of the mandrels; and, d. securing the plurality of like elements to each other to form an integral, self-supporting assembly by bonding abutting portions of cover material to the stacked elements at a plurality of locations prior to removal of the mandrels. 